TheWall Street Journal is reporting that Apple's Greg Christie, head of the iOS human interface team and one of the earliest employees to work on the original iPhone, will be retiring from the company after 18 years. Christie's former team, which currently reports to software engineering SVP Craig Federighi, will begin reporting to design chief Jony Ive instead. Christie originally joined Apple in 1996 to work on the Newton, an ill-fated early digital assistant infamous for its bulk and wonky handwriting recognition.

While higher-profile execs like Ive and Federighi get much of the credit for Apple's software design, Christie's role has been made clearer in recent interviews and in testimony from Apple's ongoing patent trial with Samsung. According to one interview with The Wall Street Journal, Christie was recruited for the iPhone project by Scott Forstall in late 2004. He would then go on to invent fundamental features of the operating system, including the "slide to unlock" gesture that has been a staple on the iPhone lock screen since its inception. Christie also kept Steve Jobs apprised of the iPhone's progress in secret, twice-monthly meetings in an unassuming conference room in Apple's Cupertino headquarters.

9to5Mac originally broke the news this morning, and its anonymous sources allege that Christie's departure was due to friction with Ive. The two supposedly "clashed over design direction" during the development of iOS 7, and Ive later "circumvented Christie's leadership of the team" while redesigning the operating system.

TechCrunch, on the other hand, says that "a flareup of friction was not behind this exit," and that Christie's retirement has been known internally for several weeks "and planned for even longer." That writeup also says that while no other Apple employees report to Christie directly as of this writing, he is staying on at Apple for some undetermined period of time to work on "special projects." As Apple-watcher John Gruber notes, this is hardly the behavior of an executive leaving on bad terms.

It's not clear from any of the reports where Ive's design responsibilities were supposed to end and Christie's were supposed to begin—the recent interviews focus almost entirely on the early design of the iPhone and not on any newer products. Many of Apple's arguments in the ongoing patent trial with Samsung revolve around the scope and scale of Apple's innovations and Samsung's alleged copying of those innovations. Clearly the company would like to drive that point home in the press without giving away anything that it currently has in store.

Whatever Christie's current responsibilities, this is probably the highest-profile departure from Apple's software design team since Scott Forstall was ousted in late 2012. iOS 7's bright colors, flat textures, and general lack of skeuomorphism are widely attributed to Ive, and now that Christie's team reports to him he'll exercise even greater control of the way the operating system looks and feels. Early rumors suggest that the next version of OS X will undergo a visual shift of its own—our review of Mavericks noted that the operating system felt like it was caught somewhere between the texture and ornamentation of Lion and Mountain Lion and the extreme flatness of iOS 7.

We'll likely get our first official look at the next iOS and OS X versions at Apple's Worldwide Developers Conference, which begins on June 2.

Andrew Cunningham / Andrew has a B.A. in Classics from Kenyon College and has over five years of experience in IT. His work has appeared on Charge Shot!!! and AnandTech, and he records a weekly book podcast called Overdue.